Conventionally, for the purpose of preventing ship collisions and for safety of life, various navigation assisting devices have been developed. For example, radar apparatuses provided with a TT (Target Tracking) function have been known as such navigation assisting devices. Here, to briefly describe, the TT function is for detecting a transition of a position of a target object existing around a ship provided with the TT function, based on a transition of previous radar images.
One mode of using a radar apparatus having a TT function is exemplary described here. A user can select a target object (echo signal) displayed on a radar image to display a mark at the position of the target object. Further, by using the TT function, the user can easily grasp the existing position of the selected target object.
When tracking a multiple number of target objects simultaneously, a multiple number of marks are displayed on a screen. In this case, the user may be unable to distinguish between the target objects and get confused. JP2501813B discloses a target object tracking device that can distinguish between the target objects in such a case.
The target object tracking device of JP2501813B includes the tracking means and a discriminating mark generating means. The tracking means calculates a position and a speed of a target object and outputs them to the discriminating mark generating means along with target object numbers. The discriminating mark generating means stores a relation between the target object number and a discriminating number. The discriminating number is generally a number displayed in vicinity of the target object on display. That is, the discriminating number is a displayed object used to discriminate the target object, and therefore, it corresponds to the mark described above. The user can distinguish to grasp a plurality of target objects by referring to the discriminating numbers.
Note that, JP2501813B also discloses a configuration for changing a color and the like of the displayed mark depending on how dangerous the target object is.
Although JP2501813B discloses the process of storing the relation between the target object number and the discriminating number, it does not disclose the method of establishing and changing (editing) the relation.
Therefore, the user may get confused in a case where the target object to start the tracking thereof is failed is selected again, a new target object number (different from the previous target object number) is assigned to the target object, and a new discriminating number (different from the previous discriminating number) is displayed.
Note that, with general radar apparatuses having the TT function, by selecting a mark and selecting a predetermined setting item, the display mode of the mark can be changed as the user desires. The above problems can be solved by using this function. However, in this method, the display mode of the mark can only be changed one by one, and as the number of the marks increases, it becomes more time consuming.